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Chapter 26.Origin of Life

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The historical tree of life can be documented with evidence.

The Origin of Life on Earth is another story…

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Origin of Life hypothesis Abiotic synthesis of organic molecules

amino acids & nucleotides Building polymers

joining molecules into polymers proteins & nucleic acids

Protobionts packaging polymers into membrane-

bound droplets maintain internal chemistry

Origin of self-replicating molecules makes inheritance possible

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Conditions on early Earth Reducing atmosphere

electron-adding water vapor, CO2, nitrogen, NOx, CH4,

NH3, H2, H2S

Energy source lightning, UV radiation, volcanic

What’smissing from

that atmosphere?!

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Abiotic synthesis Testable hypothesis

1920Oparin & Haldane propose reducing atmosphere hypothesis

1953Miller & Urey test the hypothesis

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Stanley Miller

University of Chicago

yieldedamino acids

hydrocarbonsN bases

other organic molecules

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Protobionts Life reproduction & metabolism

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RNA world RNA is likely first genetic material

multi-functional molecule codes information enzyme functions

ribozymes replication

regulatory molecule transport molecule

Dawn of natural selection

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Key Events in Origin of Life Key events in

evolutionary history of life on Earth life originated

3.5–4.0 bya

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Prokaryotes Prokaryotes dominated life

on Earth from 3.5–2.0 bya

3.5 billion year old fossil of bacteria modern bacteria

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Stromatolitesfossilized mats of prokaryotes resemble modern microbial colonies

Lynn Margulis

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Oxygen atmosphere Oxygen begins to accumulate 2.7 bya

photosynthetic bacteria cyanobacteria (blue-green algae)

reducing oxidizing atmosphere corrosive

banded iron in rocks = rusting

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Endosymbiosis Evolution of eukaryotes

membrane bound organelles = 2.1 bya

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Cambrian explosion 543 mya

within 10–20 million years most of the major phyla of animals appear in fossil record

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Diversity of life & periods of mass extinction

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The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago

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Early mammal evolution 125 mya mammals

began to radiateout & fill niches

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Classification Linnaeus used structural similarity 1969

Robert Whittaker devised 5 Kingdom system Monera Protista Plantae Fungi Animalia

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Re-Classifying Life New groupings

molecular data challenges 5 Kingdoms Monera is too diverse

2 distinct lineages of prokaryotes Protists are too diverse

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3 Domain system Super Kingdoms

Bacteria Archaea

extremophiles = live in extreme environments Eukarya

eukaryotes

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Bacteria Archae-bacteria

AnimaliaFungiProtista Plantae

4500

4000

3500

3000

2500

2000

500

1500

0

1000

Formation of earth

Molten- hot surface ofearth becomes somewhatcooler

Oldest definite fossilsof prokaryotes

Appearance of oxygenin atmosphere

Oldest definite fossilsof eukaryotes

First multicellularorganisms

Appearance of animalsand land plants

Colonization of landby animalsPaleozoic

Mesozoic

Cenozoic

Mill

ion

s o

f y

ears

ag

o

AR

CH

EA

N PR

EC

AM

BR

IAN

PR

OT

ER

OZ

OIC

PH

AN

ER

OZ

OC

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KingdomProtista

KingdomFungi

KingdomPlantae

KingdomAnimalia

KingdomArchaebacteria

KingdomBacteria

2005-2006 AP Biology

Any Questions??